The present invention relates to a coil unit, and more particularly, to a coil unit including a toroidal core and a bifilar coil wound over the core. The bifilar coil is an electromagnetic coil that contains two closely spaced, parallel windings.
A common-mode noise filter has been known as a coil unit including a toroidal core and a bifilar winding mounted on the core. In the coil unit, the toroidal core is shaped as designed, and the windings constituting the bifilar winding have a designated number of turns each extending for prescribed path distances and being led out at specified position, so that produced coil units can acquire uniform characteristics such as resonance frequency characteristic to one another. Such conventional coil unit is described in laid-open Japanese Patent Application Publication No. 5-275253.
As the technology advances, more precise control to signals flowing through an electronic device is required. Hence, noise should be removed from the signals at high precision. The conventional coil units have provided improved precision, but variation in characteristics is still recognized. Before using a conventional coil unit in order to remove noise from signals at high precision, the characteristics of each coil unit need to be checked, and coil units must be selectively used dependent on difference in electronic device.